Replacement of fish meal as the primary protein source in diets for farmed carnivorous fish is a major priority for sustainability of the aquaculture industry. Three plant-based protein sources (soybeans, field peas, and canola) were investigated to compare their effects on the health and performance of rainbow trout (Oncorhynchus mykiss) and to identify significant anti-nutritional factors (ANFs). Six separate 8-week studies were conducted, over a period of one year, to assess the effects of protein source and processing level (meal versus protein concentrate) at dietary inclusion rates of 0 to 300 g kg-1. Abundance of inflammatory and immune marker transcripts including proliferating cell nuclear antigen (PCNA), immunoglobulin M (IgM), interleukin-1 beta (IL-1β), interleukin-8 (IL-8), and interleukin-10 (IL-10) was evaluated in distal intestinal tissue by quantitative PCR (qPCR) analysis. Activity of the pro-apoptotic enzyme caspase-3 was also assayed in distal intestinal tissue. Transcript abundance was highly variable and no suitable genes for the internal normalization of qPCR data could be identified. As a result, transcript copy numbers were reported per 50 ng of total RNA. At 300 g kg-1 inclusion, soybean meal (SBM) increased abundance of IL-8 and IgM, pea meal (PM) increased abundance of IL-10, and canola protein concentrate (CPC) increased abundance of IL-8. Pea protein concentrate (PPC) reduced IL-8 abundance and caspase-3 activity, while increasing abundance of IL-10. Canola meal (CM) and soy protein concentrate (SPC) did not significantly affect the transcript abundance of any assayed gene. Pearson correlation coefficients were determined between gene transcript abundance, performance parameters, protein source, inclusion level, and ANF content. Specific growth rate (SGR) was negatively correlated with the abundance of IL-1β and IgM. Dietary inclusion of SBM was positively correlated with all assayed proinflammatory markers and negatively correlated with SGR. Inclusion of PM was positively correlated with both SGR and the abundance of IL-10. The inclusion of CM was negatively correlated with average daily feed intake (ADFI) and with the abundance of both IL-8 and PCNA. Inclusion of PPC correlated positively with SGR and negatively with the activity of caspase-3. Correlation between transcript abundance and dietary content of putative ANFs suggested negative correlations between glucosinolate content, proinflammatory cytokine expression, SGR, and ADFI; whereas, isoflavone content was positively correlated with proinflammatory markers and negatively correlated with SGR. In conclusion, although high SBM and CM inclusion levels have been associated with reduced growth performance in trout, only SBM was associated with increased abundance of inflammatory marker transcripts. These contrasting responses may be mediated by CM glucosinolates, which could negatively affect palatability without inducing a pro-inflammatory response. Dietary PM was very well tolerated and may have promoted anti-inflammatory activity. Further processing of protein meals to concentrates markedly reduced any observable negative impact on performance parameters and the abundance of inflammatory marker mRNA transcripts. Interestingly, both PM and PPC were positively correlated with SGR and may contain a beneficial anti-inflammatory component.

The effect of inclusion rate of pea meal (PM), pea protein concentrate (PPC), soybean meal (SBM), soy protein concentrate (SPC), canola meal (CM) and canola protein concentrate (CPC) in salmonid diets was determined through six corresponding meta-analyses of all data available in the literature for these six feed ingredients, which was followed by weighted regression analysis. Increasing dietary inclusion levels of SBM, SPC, CM and CPC reduced specific growth rate (SGR). Regression analysis determined all of these relationships to be linear declines in SGR (P < 0.05). Inclusion levels of PM or PPC did not influence salmonid SGR (P > 0.05). These results showed that the influence plant proteins have on salmonid SGR is dependent on ingredient type and inclusion level. PM, PPC, SBM, SPC, CM an aqueous-extracted CPC and a high phytate CPC (PCPC) were analyzed for chemical nutrient (proximate, amino acid and phosphorus analysis) and antinutrient composition and total tract digestibility (two separate digestibility trials) in rainbow trout (Oncorhynchus mykiss). The digestibility of proximate chemical components and amino acids were significantly higher for the soy products than the pea products. These digestibilities were also significantly higher in protein concentrates than in plant meals. Dry matter and gross energy digestibility was higher in CPC than in CM (P < 0.05). Phosphorus digestibility was higher in CPC-fed fish than in CM-fed fish (P < 0.05), which is likely due to the fact that CPC did not contain phytic acid. Six consecutive growth studies (one trial per test ingredient) were conducted over a 361-day period to determine the effects of feeding increasing inclusion rates of PM, PPC, SBM, SPC, CM and CPC on the growth performance of rainbow trout. Diets were formulated based on the digestible nutrient content of all ingredients as determined in the previously conducted digestibility trials, to contain 0, 75, 150, 225 or 300 g/kg of each test ingredient. All diets were nutritionally equal and contained 17.6 MJ/kg digestible energy, 386.2 g/kg digestible crude protein and were balanced for digestible essential amino acids to meet or exceed the requirements of rainbow trout. Linear and quadratic analysis was conducted on the experimental data. There were no significant regressions resulting from feeding PM, SPC or CPC at 0-300 g/kg for average daily feed intake (ADFI), specific growth rate (SGR), feed conversion ratio (FCR) or protein efficiency ratio (PER). A positive relationship was associated between PPC inclusion and ADFI (P < 0.05). There was a significantly negative quadratic equation associated with the inclusion level of SBM on SGR and FCR and significantly negative linear and quadratic equations for PER. There were significantly negative linear relationships between the inclusion rate of CM and the SGR, FCR and PER of rainbow trout (P < 0.05). Growth trial results suggest at inclusion levels up to 300 g/kg, PM, PPC, SPC and CPC are feasible plant-based fish meal replacements with predictable growth effects, provided the nutritional constraints set in this experiment are followed. The results of these growth experiments were further analyzed using structural equation modeling to determine the relationship between ANF in the six ingredients and ADFI and SGR, which were transformed (tSGR and tADFI, respectively) to enable comparisons between experiments. All possible models between ingredient ANF (starch, phytic acid, glucosinolates, tannins, isoflavones, total NSP, soluble NSP, insoluble NSP and saponins) and ADFI and SGR were calculated. The model with the highest likelihood, as determined by the Akaike Information Criteria0, contained 29 parameters and six degrees of freedom. tADFI positively influenced tSGR. Glucosinolates, saponins, and phytates had a significantly negative impact on tADFI, whereas tannins had a significantly positive impact. The presence of saponins in the diet resulted in a decrease in tSGR. This structural equation model had significant correlations between all ANF, with the exception of phytates and saponins. Future applications of this work will be to develop a nutritional model for optimal inclusion of plant-based feed ingredients in rainbow trout diets, based on their ANF content, which may improve the accuracy of diet formulation and growth prediction.